On every hill in the graph, the value of $\displaystyle{\sin{\theta}}\usepackage{cmbright}\Huge\$ first goes up from 0 to 1. At some point in between, it has the value $\displaystyle\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ . Then on the other side of the hill, the value of $\displaystyle{\sin{\theta}}\usepackage{cmbright}\Huge\$ goes down from 1 to 0. At some point in between, it again has the value $\displaystyle\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ . Because the sine function equals $\displaystyle\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ at two points on each hill, and because there are two hills in the interval $\displaystyle{\left[-{2}\pi,{2}\pi\right]}\usepackage{cmbright}\Huge\$ , there are a total of 4 points where $\displaystyle{\sin{\theta}}=\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ .